The present invention relates to a ferrule that is a plug side member included in an optical connector for optical connection, and to a ferrule tubular body that is a member included in the ferrule.
To optically connect the end portions of optical fibers to each other, an optical connector is used, which includes a plug for fixing the end portions of the optical fibers and an adaptor fitted to the plug from respective opposite sides. The aforementioned optical connector is classified into various types such as SC type, MU type and so on, and employs an eccentric adjustment in order to eliminate an insertion loss (a loss of optical signals) in optical connection as much as possible.
The eccentric adjustment method which has been employed conventionally will be described with reference to FIGS. 6 and 7. First, as shown in FIG. 6, a flanged member 82, which is formed with key grooves 82a at angular intervals of 90 degrees, is securely fixed to the rear end portion of a ferrule tubular body 81, and an optical fiber F1 that appears by removing a sheath of one end of an optical cord F by a predetermined length is inserted into and securely fixed to a through-hole 81a, so that the optical cord F having a required length is set to be connected to the ferrule 8.
A measurement device 9 as shown in FIG. 7 will be described briefly. The measurement device 9 includes a light source section 91, an adjust plug 93 connected to the light source section 91 through an adjust cord 92 so as to make an optical axis eccentric in a predetermined direction, an adaptor 94 for facing and engaging the adjust plug 93 and the ferrule 8 with each other, and optical power-meter 95 for measuring the luminous energy. On the ferrule side of the adaptor 94, one key (not-shown) for engagement with the key groove 7a is provided in order to indicate the eccentric direction of the adjust plug 93.
The measuring device 9 thus constructed is set such that the ferrule 8 is engaged with the adaptor 94 with the key groove 82a matched with the key as well as the open end portion of the optical cord F is connected to the optical power-meter 95. Then, the light is turned on, and a value indicated by the optical power-meter 95 is read. Next, the ferrule 8 is removed from the adaptor 94, rotated by 90 degrees, and again engaged with the adaptor 94, so that a value indicated by the optical power-meter 95 is read.
Further, this procedure is repeated twice, and a mark is applied to a key groove 82a that causes the value of the optical power-meter 95 to be maximum (the luminous energy to be maximum). Thereafter, the assembly is carried out to a housing of a desired external appearance, such as the SC type, MU type or the like, which is provided with a key indicating the eccentric direction, so that the marked key groove 82a is aligned with the key.
As explained above, in the conventional art, the eccentric adjustment is performed such that the optical connection is established actually in a state in which the optical cord F having a required length is connected to the ferrule 8. Through the aforementioned process, plugs which are lower in insertion loss with respect to the adjust plug 93 whose optical axis is eccentric at a predetermined amount are mass-produced. By using these plugs, an optical connection always stabilized in insertion loss can be realized.
The eccentric adjustment in accordance with this system is preferable in view of the fact that an optical connection always stabilized in insertion loss can be realized. However, the adjustment needs the insertion and removal of the ferrule into and out of the adaptor, and thus it has been pointed out that the end face of the ferrule may roughened, which causes a problem in the process.
Further, it is impossible to realize an optical connection in which the insertion loss is further reduced by the adjustment of this system in which, as mentioned above, the luminous energy is measured at intervals of every 90 degrees (four-equi-angular-interval distribution) using the key engagement with respect to the adjust plug whose optical axis is made eccentric at the predetermined amount and the direction (the key groove) at which the insertion loss is the smallest among them is regarded as the eccentric direction.
Accordingly, it is an object of the present invention to provide a ferrule tubular body and a ferrule which is free from the fear that the end face of the ferrule may be roughened, which can eliminate the eccentric adjustment process performed after the optical fiber is fixed, and which can attain an optical connection in which the insertion loss is further reduced.
A first aspect of the present invention for solving the aforementioned problems is embodied in a ferrule tubular body having a through-hole to which an end portion of an optical fiber is inserted to be held, the ferrule tubular body being characterized by including an indicator section for indicating an eccentric direction of the through-hole with respect to a center of an outer circumference of the body.
A second aspect of the present invention is based on the ferrule tubular body as set forth in the first mode, and is characterized in that the indicator section is a visual indication provided on an outer circumferential surface of the ferrule tubular body.
A third aspect of the present invention is based on the ferrule tubular body as set forth in the first mode, and is characterized in that the ferrule indicator section is a recess provided in an outer circumferential surface of the ferrule tubular body.
A fourth aspect of the present invention is based on the ferrule tubular body as set forth in the second or third mode, and is characterized in that the indicator section is provided on at least one of a leading end portion and a rear end portion of the ferrule tubular body.
A fifth aspect of the present invention is embodied in a ferrule including a ferrule tubular body having a through-hole to which an end portion of an optical fiber is inserted to be held, and a flanged member securely fixed to a rear end portion of the ferrule tubular body, the ferrule being characterized in that an indicator section indicating an eccentric direction of the through-hole with respect to a center of an outer circumference of the ferrule tubular body is provided on at least one of the ferrule tubular body and the flanged member.
A sixth aspect of the present invention is based the ferrule as set forth in the fifth mode, and is characterized in that the indicator section is an indication or a recess provided on a leading end of the ferrule.
A seventh aspect of the present invention is based on the ferrule as set forth in the fifth mode, and is characterized in that the indicator section is a visual indication or a recess provided on the flanged member.
As factors of this eccentricity hindering the optical connection, it can be pointed out the following; e.g. that an optical fiber is not held at the center of a through-hole of a ferrule, a core is not positioned at the center of the optical fiber, a through-hole is not opened at the center of the outer circumference of a ferrule tubular body, and so on. The eccentricities in the held position of optical fiber with respect to the through-hole of the ferrule and the position of the core within the optical fiber are minute and thus can be disregarded in contrast to the eccentricity in the position of the through-hole in the ferrule. Accordingly, since the present invention makes it possible to recognize the eccentric direction of the through-hole, the eccentric adjustment with high precision in comparison with the conventional eccentric adjustment can be realized.
In addition, it is not essential to provide the indicator sections noted above in the eccentric direction of the through-hole with respect to the center of the outer circumference of the ferrule tubular body. That is, it suffices that the eccentric direction of the through-hole can be observed relatively from the external side.